1. Field of the Invention
The present invention relates to a link type variable stroke engine, and especially relates to a link type variable stroke engine in which, in a crankcase of an engine main body, a crankshaft is rotatably supported, and a rotary shaft is rotatably supported so that power reduced at a speed reduction ratio of 1/2 from the crankshaft is transmitted thereto, the rotary shaft having an axis parallel with the crankshaft and being provided with an eccentric shaft at an eccentric position, and a piston, slidably fitted to a cylinder block of the engine main body, the crankshaft and the eccentric shaft are linked by a linking mechanism, the linking mechanism including: a main connecting rod coupled, at one end, with the piston by using a piston pin; a sub connecting rod rotatably coupled with a crank pin of the crankshaft and rotatably coupled with the other end of the main connecting rod by using a connecting rod pin; and a swing rod rotatably coupled, at one end, with the sub connecting rod by using a swing pin at a position displaced from a position coupled with the main connecting rod and rotatably coupled, at the other end, with the eccentric shaft.
2. Description of the Related Art
Inertial exciting forces, which induce inertial vibration, of a conventional reciprocating engine are only integer order components, i.e., a first order component, a second order component, a third order component . . . , of a rotation speed of a crankshaft. To suppress and lessen first order vibration and second order vibration, such a reciprocating engine includes a first order balancer and a second order balancer which reduce the inertial exciting forces in synchronization with rotation of the crankshaft.
Meanwhile, a link type variable stroke engine has already been known by Japanese Utility Model Publication No. 57-32267, Japanese Patent Application Laid-open No. 9-228858, the specification of U.S. Pat. No. 4,517,931, and the like. In the link type variable stroke engine, a piston, a crankshaft and an eccentric shaft are linked by a linking mechanism, the eccentric shaft provided to a rotary shaft which is parallel with the crankshaft and to which power reduced at a speed reduction ratio of 1/2 from the crankshaft is transmitted. Even in such a link type variable stroke engine, inertial exciting force needs to be suppressed and lessened.
Now, in a link type variable stroke engine, an eccentric shaft is rotated in synchronization with a crankshaft at a speed reduction ratio of 1/2. For this reason, half-order rotational inertial force occurs at the eccentric shaft. However, none of the above-described disclosed Japanese Utility Model Publication No. 57-32267, Japanese Patent Application Laid-open No. 9-228858 nor the specification of U.S. Pat. No. 4,517,931 mentions the half-order rotational inertial force or discloses any method for suppressing and lessening the half-order rotational inertial force. This half-order inertial exciting force is an inertial exciting force having an order which does not occur in the conventional reciprocating engine, and has a frequency which is half of that of the first order vibration, that is, a low frequency. Accordingly, the half-order inertial exciting force is perceived as muffled sound or uncomfortable vibration different from conventional ones, and is thus not preferable from the view point of marketability. In addition, conventional integer order balancers, such as the first order balancer and the second order balancer, do not have an order suitable for the half-order inertial exciting force, and are hence not effective for the half-order inertial exciting force.
For this reason, when the inertial exciting force becomes excessively large and consequently the inertial vibration becomes large, a worker using an apparatus equipped with the link type variable stroke engine, for example, a working machine, feels uncomfortable, the working machine starts to move by itself and thereby grounding performance is deteriorated, and noise attributable to vibration increases, for example. Moreover, an excessive increase in the inertial exciting force may also cause a reduction in the strength of components of the engine.